This invention relates to a photosensitive composition, particularly to a photosensitive composition suitable for preparation of nega-type photosensitive lithographic printing plate.
Photosensitive printing plates are generally obtained by coating a photosensitive composition on a support such as aluminum plate, etc., irradiating an active ray such as UV-ray through a negative image, etc. to polymerize or crosslink the portion irradiated with the light, thereby insolubilizing said portion in a developer, dissolving out the non-irradiated portion into a developer, thereby making the respective portions an image portion which repels water and receives an oily ink and a non-image portion which receives water and repels the oily ink.
As the photosensitive composition in this case, particularly in nega-type PS plates, there have been widely employed diazo resins such as condensates of p-diazodiphenylamine and formaldehyde.
On the other hand, Japanese Unexamined Patent Publication No. 115150/1977 discloses a technique for preventing polymerization inhibition with oxygen during image exposure by addition of a diazo resin in a photopolymerizable photosensitive composition.
However, the compositions according to the techniques of the prior art are not sufficient in sensitivity and chemical resistance. Besides, even by the technique in the above publication, the influence from oxygen could not be fully precluded.
Accordingly, a main object of the present invention is to provide a photosensitive composition, which is not only excellent in sensitivity and chemical resistance, but also can prevent surely polymerization inhibition with oxygen, and therefore is suitable particularly for nega-type photosensitive printing plate.